Process of cleaning screens



R. G. WOODBRIDGE, JR. PROCESS OF CLEANING SCREENS.

APPLICATION FILED MAY 31, 1911.

1,367, 1 1 1 Patented Feb. 1, 1921.

DEN]

UUUDUDDEI DEIEIEIEIEICIEID UDUUUEIEID INVE/VTUI? A Tram/HS UNITED STATESI RICHARD G. WOOIDIBRIIJGE, JR., F WILMINGTON, DELAWARE, ASSIGNOR TO E.I. DU

PATENT OFFICE.

PONT DE NEMOURS AND COMPANY, OF WILMINGTON, DELAWARE, A CORPORA- TION OFDELAWARE PROCESS OF CLEANING SCREENS.

Specification of Letters latent.

Patented Feb. 1, 1921.

Application filed May 31, 1917. Serial No. 171,999.

To all whom it may concern."

Be it known that I, RICHARD Gr. WOOD- nnmen, J r., of Wilmington, in thecounty of New Castle and in the State of Delaware, have invented acertain new and useful Improvement in Processes of Cleaning Screens, anddo hereby declare that the following is a full, clear, and exactdescription thereof. My invention relates particularly to a' process ofcleaning screens used in the manufacture of nitrocellulose ornitrocellulose compositions, although it is applicable to otherpurposes.

The object of my invention is to provide a process for cleaning screensas, for example, screens made of wire mesh or perforated plates, so asto remove the colloided or uncolloided nitrocellulose thereirom whichhas accumulated in the screening process in the manufacture ofn1trocellulose or nitrocellulose compositions. In

the process of making nitrocellulose orv nitrocellulose compositions,the nitrocellulose, or composition containingthe same, is

till

passed through one or more screens which may be of woven wire orperforated metal, or .both, and the material of which they are made mayhe steel, iron, brass or copper, the purpose being to remove all foreignmaterials such as wood, fibers, hair, sand, metallio particles, etc.From time to time it therefore becomes necessary to clean these screensin order to remove the accumulated foreign materials and adheringnitrocellulose or nitrocellulose composition. The usual method to cleanthese screens has been to set fire to the nitrocellulose ornitrocellulose composition. This burning process makes themetal brittleand in consequence the screens can only he used a relatively few timesbefore discarding, as each burning treatment tends to make the screensmore brittle. Another method of removing nitro amounts of nitrocelluloseand nitrocellulose compositions, as in this case, are decomposed.However, I have discovered that there is little or no danger in theoperation, provided the process is carried out as here inafter describedand, furthermore, that the tensile strength of the metal composing thescreen is practically uninjured by my process, thereby making itpossible to use the screens many more times before discarding, than hasheretofore been possible. It is the object of my invention toremove-these adhering materials from the screens in such a manner as toavoid damage to the screens as far as possible. A further object of myinvention is to remove such adhering materials from the screens byapplying thereto a salt solution having an alkaline reaction, and whichis of such a nature that it'efi'ectively nemoves the nitrocelluloseor-composition containing the same, and thus removes the bulk of theforeign materials and loosens the remaining foreign materials in themeshes of the screens and without attacking, to any detrimental extent,the screens themselves. An object of my invention is thus to make use ofsolutions of alkali hydroxids, sulficls or carbonates, or hydroxids orsulfids of the alkali earth metals. A further object is to removethe-remaining foreign particles after such treatment, by the use of arotating brush. A further object is to restore the screens to theiroriginal shape as byof my invention will appear from the detaileddescription thereot contained herein after, it being important that thecleaning shall be executed at a temperature and at a concentration highenough to attack and remove the nitrocellulose or nitrocellulosecomposition without causing any appreciable attack upon the metal of thes reen.

l Vhile my invention is capable'ofembodirneut in many difierent forms,for the purpose of illustration I shall descrlbe onlycertain forms of myinvention hereinafter, and I have shown only one form of apparatus whichmay be used in connection with my invention in the accompanying drawing,in which-- The figure is a vertical Section of an apparatus which maybeused in connection with my- 1nvent1on.

,n the drawing I have shown an iron or steel tank 1, provided with afalse bottom or iron grating 2, near the bottom thereof, said tank beingprovided with a valved inlet 3 for water and a valved inlet 4 for steamat baskets 5 with the screens 7 therein which have been used in thescreening operation in the production of nitrocellulose ornitrocellulose compositions, have been placed in the tank 1, said tankis partially filled with caustic soda solution containing from 25% to30% of sodium hydroxid by weight, dissolved in water. Any desired gradeof caustic soda may be used. The caustic soda solution is then heated bythe introduction of, steam from the pipe 4 until the solution has atemperature of preferably from to C.. The caustic soda'thereupon attacksthe colloided and uncolloided nitrocellulose vigorously, thusdecomposing and entirely removing the same from the screens in fromthirty minutes to two hours, de-

pending upon the thickness of the accumulated nitrocellulose ornitrocellulose composition, also.upon the percentage of solventscontained in the nitrocellulose composition, and upon the temperatureofv the caustic soda solution, also upon the strength of the causticsoda solution. The strength of the causticfsoda solution may be above30% but a 30% solution enables the removal of the materials from thescreens to be carried out with sufiicient rapidity. The solution ofcaustic soda may be used and reused until the strength is reduced tofrom 3% to 4% sodium hydroxid by weight, whereupon the solution may beeither strengthened up to 30% by the addition of fresh caustic soda, ordiscarded altogether. The caustic soda solution will in this way removevery nearly all of the foreign materials on the screens and, inaddition, the nitrocellulose or nitrocellulose composition adhering tothe screens. The baskets 5 are then ordinarily removed from the solutionand subjected to washing with water and drying in a current of hot air.Any of the foreign materials such as wood, fibers, hair, sand, metallicparticles, etc., which remain entangled in the meshes of the screens,and which are left therein after the greater amount of the same havebeen removed in the preceding steps of the process, are loosely held inthe meshes or perforations of the screens and can readily be removedtherefrom by brushing as, for example, with a rotary brush. The screenscan then be straightened in any suitable manner as, for example, bypassing through a pair of rolls. The process as just described isparticularly applicable to screens made of steel or iron, inasmuch asthe caustic soda solution has no appreciable action thereon. However,the process is also applicable to copper, brass and phosphor bronzescreens, in which case I )refer to use a caustic soda solution initiallyweaker than 30% by weight, but I do not limit myself to any particularstrength, it being obvious that I would use that strength of solutionparticularly adapted for removing the nitrocellulose or nitrocellulosecomposition with the minimum detrimental action on the screens, and thatI would remove the screens from the solution before it had time to reactupon the metal of the screen to a detrimental extent. Furthermore, itwill be-understood that a number of different decomposing agents may beused instead of the caustic soda as, for example, caustic potash, alkalisulfids, alkali carbonates and hydroxids and sulfids of the alkali earthmetals, or mixtures of the same. Screens which have been cleaned in thismanner may be used a great many times by being repeatedly cleaned.

While I have described my invention above in'detail, I wish it to beunderstood that many changes may be made therein without departing fromthe spirit of the same.

I claim:-

1. The process of cleaning without appreciably attacking metallicscreens through which nitrocellulose compositions have been passed,which comprises decomposing the nitrocellulose adhering to the screenthrough the application of a salt solution having an alkallne reactionwhile controlling the intensity of the reaction by regulating thetemperature and the concentration.

The process of cleaning without appreciably attacking metallic screensthrough which nitrocellulose compositions have been passed, which comrises decomposing the nitrocellulose adheringto the screen through theapplication of a caustic soda solution while controlling the intensityof the reaction by regulating the temperature and the concentration.

3. The process of cleaning without appreciably attacking metallicscreens through which nitrocellulose compositions have been passed,which comprises decomposing the nitrocellulose adhering to the screenthrough the application of a caustic soda solution at a temperatureapproximately between 70 and 80 C.

4. The process of cleaning without appreciably attacking metallicscreens through ioo which nitrocellulose compositions have been passed,which comprises decomposing the nitrocellulose adhering to the screen byimmersing the screen in a salt solution having an alkaline reactionWhile controlling the intensity of the reaction by regulating thetemperature and the concentration.

5. The process of cleaning without appreciably attacking metallicscreens through which nitrocellulose compositions have been passed,which comprises decomposing the nitrocellulose adhering to the screen byimmersing the screen in a caustic soda solution While controlling theintensity of the reaction by regulating the temperature and theconcentration.

6. The process of cleaning without appreciably attacking metallicscreens through which nitrocellulose compositions have been passed,which comprises decomposing the nitrocellulose adhering to the screen byimmersing the screen in a caustic soda solution at a temperature in theneighborhood of 80 C.

7. The process of cleaning without appreciably attacking metallicscreens through which nitrocellulose compositions have been passed,which comprises decomposing the ni-' trocellulose adhering to the screenthrough the application at a temperature high enough to attack thenitrocellulose without appreciably attacking the metal of a saltsolution having an alkaline reaction, washing the screen, and brushingthe residue therefrom.

In testimony that I claim the foregoing I have hereunto set my hand.

RICHARD G. WOODBRIDGE, J R.

Witnesses:

G. D. HOPKINS, A. M. GORMAN.

